In an observatory unlike any other in the world, deep beneath China’s Guangdong Province, the world’s largest neutrino detector has begun operations.
The 20,000-ton liquid scintillator detector at China’s Jiangmen Underground Neutrino Observatory (JUNO) has now completed filling, according to a statement from the Chinese Academy of Sciences Headquarters. The launch of the new facility marks the culmination of a period spanning more than a decade, encompassing the observatory’s construction phase and other preparatory efforts in advance of operations.
Now, with JUNO’s official launch, a new era of physics experiments involving mysterious “ghost particles” known as neutrinos—and very large ones—is about to take shape within the gigantic spherical observatory.
An Underground Neutrino Observatory
Initial trials at the facility are showing that the tests meet or exceed expectations for its operations, which physicists hope will bring us closer to confirming the existence of a third mass state that could be heavier than the second currently known to scientists.
The JUNO facility, which began operations recently at a depth of 700 meters beneath nearby Jiangmen City, is the massive detection component that registers antineutrinos originating from the Taishan and Yangjiang nuclear power plants located more than 50 kilometers away.
JUNO is capable of high-precision measurements that place its capabilities far beyond those of the most precise neutrino oscillation facilities already in existence. In the years ahead, it will facilitate some of the most advanced capabilities ever observed with such measurements.
At the heart of the state-of-the-art JUNO facility is a massive 20,000-ton liquid-scintillator detector, which rests at the center of an equally large, 44-meter-deep pool of water. The 35.4-meter acrylic sphere is supported within the tank, along with the scintillator and other components of the device, by a stainless-steel support truss spanning more than 40 meters.
When neutrino interactions are detected as a result of light arising from scintillation, they are converted into electrical signals. Thanks to its unique design, the facility is custom-made for next-generation studies of neutrinos from our Sun and from within Earth’s atmosphere, as well as from more distant cosmic locales such as supernovae.
Unknown Physics
Arguably, one of the most exciting prospects involving JUNO’s capabilities is how it may expand our knowledge of physics by advancing physicists’ searches for phenomena like sterile neutrinos, a variety of hypothetical particles whose only known interactions are related to gravity, as well as the decay of protons.
“Completing the filling of the JUNO detector and starting data taking marks a historic milestone,” said Prof. Yifang Wang, a researcher at the Institute of High Energy Physics (IHEP) at the Chinese Academy of Sciences and a spokesperson for JUNO, who said that the detector’s competion marks a “historic milestone,” adding that its operations could lead to answers for some of the most exciting mysteries in physics today.
“For the first time, we have in operation a detector of this scale and precision dedicated to neutrinos,” Wang said in a statement. “JUNO will allow us to answer fundamental questions about the nature of matter and the universe.”
The Long Road to the Future
However, the project’s development, which began a decade ago, has been anything but easy.
“Building JUNO has been a journey of extraordinary challenges,” said Professor M.A. Xiaoyan, the Chief Engineer with JUNO, who explained that completion of the next-generation detector “demanded not only new ideas and technologies, but also years of careful planning, testing, and perseverance.”
Altogether, producing a facility that could meet the demands for stability and purity, while also ensuring safety once it commenced operations, was an endeavor that required the work of hundreds of experts from various fields over the last decade.
Now that it is functional, the facility is poised to fundamentally change how we think about the neutrino and related phenomena, according to Prof. Gioacchino Ranucci, a Professor at the University of Milano and INFN-Milano and a Deputy spokesperson for JUNO.
“The worldwide liquid scintillator community has pushed the technology to its ultimate frontier, opening the path towards the ambitious physics goals of the experiment,” Ranucci said in a statement.
In the years ahead, JUNO’s mission could ultimately reveal answers to longstanding questions, such as whether neutrinos are Majorana particles —a type of fermion possessing its own antiparticle. Such a revelation could help to resolve major questions in the fields of not just particle physics, but also astrophysics and cosmology, offering profound insights that could reshape our concepts of the universe.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. A longtime reporter on science, defense, and technology with a focus on space and astronomy, he can be reached at micah@thedebrief.org. Follow him on X @MicahHanks, and at micahhanks.com.